The instant invention relates to hole cutting tools for metal and more particularly to a novel hole cutting tool for metal having removable cutting inserts.
Hole cutting tools for cutting circular holes in most types of materials generally fall into two major categories; those which operate by cutting or removing the entire interior area of a circle and those which operate by cutting only the circumferential areas of a circle thereby producing an interior circular plug during a cutting operation. A conventional drill is an example of the former type of tool, i.e., a drill which in effect chisels or shaves the entire interior of a circle as it rotates to produce a desired hole. A variety of different types of drills and cutting tools which operate by this general principle have heretofore been available for various applications for cutting holes of all sizes. Several types of cutting tools have also heretofore been available for cutting holes by cutting or shaving only the circumferential areas thereof, conventional hole saws and tools known as trepanning tools being exemplary in this regard. Tools of this type have advantages over conventional drilling tools by virture of the fact that they require substantially less cutting to achieve a desired hole and hence hole cutting can be effected substantially faster and with substantially less energy consumption when using these tools than when using conventional drilling tools.
The use of trepanning tools which cut only the circumferential areas of circles, to cut large diameter holes of substantial depths is widely known. In this regard, conventional trepanning tools comprise an elongated tubular cutting head having a single cutting blade or bit secured thereto which engages a work piece to shave or cut portions thereof to define the circumference of a circle upon rotation of the tool. Accordingly, as cutting of a work piece is effected, a center plug is produced which is received in the center area of the elongated tubular cutting head. The cutting of holes having depth to diameter ratios of up to 100 to 1 can be effected with tools of this type, the elongated plugs thereby produced being received in the tubular cutting heads of the respective tools. Tools of this type have been available for cutting holes having diameters ranging from approximately one inch to holes having extremely large diameters, for example up to 10 feet or more. Many of the larger trepanning tools heretofore available have been provided with removable bits or cutting inserts which can be removed for sharpening or replacement thereof to provide extended tool life. However, the use of removable bits or inserts has heretofore proven to be impractical with smaller diameter tools due to the lack of availability of the effective means for securing and retaining cutting inserts in cutting heads of smaller diameter tools. This is primarily due to the fact that the differences between the cutting speeds at the inner and outer portions of a circular cut cause resultant forces on a cutting bit or insert which tend to make it yaw outwardly. The heretofore known insert retaining means have simply been ineffective at counteracting these forces when embodied in smaller sizes and hence, the heretofore known trepanning tools having diameters of approximately three inches or less have been provided with cutting bits which are welded or brazed in place and therefore cannot be removed for sharpening or replacement. As a result, when the cutting bits of tools of this type become dull and worn, the replacement of the entire tool becomes necessary.
The instant invention relates to a novel hole cutting tool which is operable to form a shallow circular hole by cutting only the circumferential areas thereof, but which can be embodied in reduced sizes with removable cutting inserts to allow the replacement or sharpening thereof. Specifically, the hole cutting tool of the instant invention comprises a tool body which is attachable to a drive apparatus for rotating the tool about an axis, a cutting head which is attached to the body, a cutting insert which is attached to the cutting head, and means which engages the leading edge of the insert to retain it in a cutting position on the cutting head. The lower portion of the cutting head is of tubular configuration and has at least one longitudinal slot therein which extends inwardly from the terminal end thereof, the slot having leading and trailing edges as determined by the cutting rotation of the tool. The trailing edge of the slot is defined by a plane which is inwardly divergent relative to the adjacent intersecting radial plane of the cutting head, and the cutting insert has a planar seating surface which is received in abutting relation with the trailing edge of the slot. The cutting edge of the cutting insert is in substantially radial relation to the cutting head and in spaced relation to the leading edge of the slot. Accordingly, due to the geometry of the cutting insert and of the slot, when forces are applied to the end of the cutting insert during a cutting operation, the insert remains securely in position and this permits the use of the instant invention in tools for cutting holes of reduced diameters, i.e., holes having substantially smaller diameters than was possible with the heretofore known inserted hole cutting tools. In the preferred embodiment of the instant invention, the means which retains the insert in the slot comprises a retaining wedge which engages the leading edge of the slot and engages the leading edge of the insert to urge it against the trailing edge of the slot so that the insert is wedged in position with the angle of the wedge and the angle of the trailing edge of the slot preventing outward movement of the insert. Further, in the preferred embodiment, three equally circumferentially spaced slots are provided in the cutting head, each having an insert received therein, whereby high speed cutting can be effected with the tool. It has been found that tools embodying these features can be used for rapidly and effectively cutting holes having reduced diameters with a minimum of energy consumption.
Accordingly, it is a primary object of the instant invention to provide a hole cutting tool having removable cutting inserts.
Another object of the instant invention is to provide a hole cutting tool having removable cutting inserts which can be used in reduced sizes.
A still further object of the instant invention is to provide a hole cutting tool wherein a removable cutting insert is effectively retained in position by means of a wedge-like retaining member.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.